The present invention relates to a sensor unit, an exposure apparatus, and a device manufacturing method.
A conventional projection exposure apparatus projects and exposes a circuit pattern of a reticle (mask) onto a wafer via a projection optical system in manufacturing a fine semiconductor device and liquid crystal display (“LCD”) device.
In the exposure apparatus, the pattern's critical dimension becomes very smaller, and each component is thoroughly improved. For example, a finer pattern is used for the measurement. A sensor unit is thus proposed which measures a focal plane of the projection optical system. See, for example, Japanese Patent Applications, Publication Nos. 2005-175400, 2005-166722, and 2000-175034.
The sensor unit, as used herein, measures a focal plane of the projection optical system by receiving, through a sensor, the light that has passed a reference mark. The reference mark has a pinhole or a slit that transmits the light. A substrate that has the reference mark also has another mark that is used to adjust a position of the reference mark before the above measurement. The other mark used for the positional adjustment of the reference mark is a reflection mark, and a position of the other mark is detected when a sensor detects the light reflected on the other mark.
Conventionally, in detecting the light that has transmitted through the reference mark, the sensor also detects the light that has transmitted through the reflection mark, such as the other mark used to adjust the position of the reference mark, and thus the S/N ratio deteriorates.
As the high measurement accuracy is increasingly demanded, the S/N ratio must be further improved. Therefore, the slight deterioration of the S/N ratio becomes non-negligible.